1. Field of the Invention.
The present invention relates to modified pigments and to processes for preparing modified pigments.
2. Description of the Related Art.
The surface of pigments contain a variety of different functional groups, and the types of groups present depend on the specific class of pigment. Several methods have been developed for grafting materials and, in particular, polymers to the surface of these pigments. For example, it has been shown that polymers can be attached to carbon blacks containing surface groups such as phenols and carboxyl groups. However, methods which rely on the inherent functionality of a pigment""s surface cannot be applied generally because not all pigments have the same specific functional groups.
Methods for the preparation of modified pigment products have also been developed which can provide a pigment with a variety of different attached functional groups. For example, U.S. Pat. No. 5,851,280 discloses methods for the attachment of organic groups, such as ionic or ionizable groups, onto pigments including, for example, attachment via a diazonium reaction wherein the organic group is part of the diazonium salt. The resulting surface-modified pigments can be used in a variety of applications, such as inks, inkjet inks, coatings, toners, plastics, rubbers, and the like.
Other methods to prepare modified pigments have also been described. For example, PCT Publication No. WO 01/51566 discloses methods of making a modified pigment by reacting a first chemical group and a second chemical group to form a pigment having attached a third chemical group. Ink compositions containing these pigments are also described.
While these methods provide modified pigments having attached groups, there remains a need for improved modified pigments as well as for processes for attaching groups and, in particular, polymeric groups, to a pigment. These additional methods may provide advantageous products and alternatives for forming modified pigments.
The present invention relates to processes for preparing modified pigments. In one embodiment, the process comprises the step of: combining, in any order, a pigment having attached an electrophilic group and a thiol reagent comprising at least one xe2x80x94SH group and at least two ionic or ionizable groups. Preferably the thiol reagent is an alkylthiol substituted with at least two carboxylic acid groups. In a second embodiment, the process comprises the step of: combining, in any order, a pigment having attached an electrophilic group and a thiopolymer comprising at least one xe2x80x94SH group and at least one ionic or ionizable group. Preferably the thiopolymer comprises the reaction product of a polymer having at least one anhydride, at least one activated carboxylic acid, or at least one carboxylic acid or salt thereof; an aminoalkane thiol or an aromatic amino thiol; and optionally an activating agent.
The present invention further relates to modified pigments. In one embodiment, the modified pigment comprises a pigment having attached a group comprising the formula xe2x80x94Sxe2x80x94[PI]. In a second embodiment, the modified pigment comprises a pigment having attached a group comprising the formula xe2x80x94X-Sp-Sxe2x80x94[PI], wherein X is an arylene, heteroarylene, or alkylene group, Sp is a spacer group. For both embodiments, PI represents an organic group substituted with at least two ionic or ionizable groups or a polymeric group comprising at least one ionic or ionizable group.
The present invention further relates to ink compositions, in particular inkjet ink compositions, comprising the modified pigments described herein.